The present invention relates to an electrophotographic copying machine and, more particularly, to a recognition and discrimination system for identifying spots or etched areas on a document platen and for preventing the reproduction of the spot or etched areas during a document copying operation.
Digital scanning techniques are well known in the art wherein documents are placed on a document glass platen and scanned by a CCD array to capture an electronic image of the document. The output of the array, representing the scanned document, can be digitized and used, for example, to drive a Raster Output Scanner at a local or remote location.
A problem in prior art machines is that any defects which exist in or on the document platen are perceived as "information" by the scanning device and incorporated when scanning a document. For example, dirt specks or portions of the platen which have become degraded (etched) by, for example, operation of a document handling feed roll system, are reproduced as black spots or marks on output copies made of documents scanned on the platen.
It is an object of the present invention to identify dirt or etch marks on a platen so as to prevent a reproduction of these marks on output copies. This object is achieved by first scanning a platen without a document thereon and storing the representative digital image in a controller memory. This reference image provides information on the presence and location of marks of dirt or etched areas on the platen and is available for performing certain logic operations with subsequent stored images made of documents which are placed on the platen. Once the mark location is determined on the stored image which represents the document that has been scanned, the spot is erased by changing pixel status from black to white. A second logical process is implemented to determine whether the spot is wholly or partially within any informational areas of the document, in which case, some or all of the spot that has been erased is restored. More particularly, the present invention relates to a method of compensating for dirt or etched areas in a document platen comprising the steps of:
scanning the platen in the absence of a document, the platen having at least one dirt or etched area on the surface thereof,
generating digital output signals representative of said scanned platen,
processing said digital output signals to create a platen bit map image of black and white pixels of said scanned platen image, said black pixels representing the dirt or etch area,
scanning the platen in the presence of a document having information content thereon,
generating digital output signals representative of said scanned document,
processing said document output signals to create a document bit map image of black and white pixels, the black pixels representing information content and the dirt or etch area,
determining the location of the dirt or etch area within the document bit map image and changing the pixels representing the dirt or etch area to white,
performing a spiral growth process function on that section of the bit map image which incorporates the recognized dirt or etch area to determine whether the area lies wholly or partly within an information content area of the document image, and
restoring the pixels from white to black values when the entire area or portion of the area is determined to lie within an information content area of the document.